1. Field of the Invention
The present invention relates to an automatic-braking control system for a motor vehicle in which, when an obstacle ahead of the vehicle has been sensed, automatic braking is applied in accordance with circumstances on that occasion.
2. Description of the Prior Art
Heretofore, in order to prevent the collision accident of a motor vehicle or the rear-end collision accident thereof, there has been proposed technology wherein an obstacle ahead of the vehicle is sensed, and wherein any warning is issued to the driver of the vehicle or the vehicle is automatically braked when the vehicle and the obstacle have approached up to a distance (a threshold value) at which the further approach thereof without any evasive action is decided or judged dangerous.
By way of example, the official gazette of Japanese Patent Application Laid-open No. 298022/11994 discloses a system wherein automatic braking is executed on the basis of the distance of the pertinent vehicle from an object ahead (a preceding vehicle) as found by a radar (that is, the distance between the two vehicles), the relative speed between the vehicles, and the speed of the pertinent vehicle. More concretely, in this system, a first threshold value at which the rear-end collision of the pertinent vehicle against the preceding vehicle can be prevented by braking, and a second threshold value at which the rear-end collision against the preceding vehicle can be prevented by a steering action, are calculated on the basis of the speed of the pertinent vehicle, the distance between the vehicles and the relative speed between them. Herein, even when the detected distance between the vehicles is less than the first threshold value, the braking is not executed as long as this distance is greater than the second threshold value, and when it has become less than or equal to both the first and second threshold values, the braking is executed for the first time. Thus, the prevention of the rear-end collision as intended by the driver is achieved.
Prior-art automatic-braking control systems including the aforecited system, however, are problematic as stated below. Even after the vehicle has been stopped by the automatic braking, this automatic braking continues to work. In case of an excessive braking force, accordingly, the vehicle is difficult to move forward (or it is sometimes incapable of movement) in spite of an accelerator pressing action done by the driver.
As a method for eliminating the problem, it is considered that the automatic braking is released after having worked for a predetermined time period. However, the automatic braking is executed irrespective of the driver's intention. Accordingly, the method has the drawback that, even when the driver intends to start the vehicle again before the release of the automatic braking, he/she fails because the automatic braking is working yet.
Another countermeasure considered is a method which releases the automatic braking upon detecting that the driver has stepped on an accelerator pedal. Herein, even in a case where the driver has erroneously pressed the accelerator pedal with the deceleration of the vehicle based on the automatic braking, the accelerator pressing action is detected as the braking releasing condition. Accordingly, this method has the drawback that the automatic braking is released in spite of being originally required.